Cars and other vehicles are usually equipped with seatbelts, airbags and other safety devices for protecting the driver and passengers from the impact at the time of a crash. In the case of a seatbelt safety device, for example, the seatbelt winding-retraction device is additionally provided with a rapid winding-retraction means, and the driver and passengers are reliably protected from the impact at the time of a crash by activating this rapid winding-retraction means at the time of an accident or other emergency so as to instantaneously retract the seatbelts. As the aforesaid rapid winding-retraction means ones have recently been widely adopted that are equipped with a mechanism for rapidly retracting the seatbelt by using an electric ignitor that is activated by the impact at the time of a crash to instantaneously drive a cylinder piston or a rotor by utilizing the pressure of combustion gas when gunpowder or the like is made to burn instantly. The wide adoption of rapid winding-retraction means equipped with such mechanisms has been accompanied by the development of many gas generators for use therein.
[Patent Document 1]
FIG. 5 is a schematic longitudinal section for explaining one conventional example of a gas generator applied to a seatbelt or other vehicle safety device, which is disclosed in Japanese Unexamined Patent Publication No. 2003-205823 (Patent Document 1).
A gas generator B is first provided with a holder 1A constituting a base. The holder 1A is formed of aluminum, and a connector insertion hole 11 is formed on the side attached to the vehicle body while a pedestal 12 for forming an ignitor unit is formed on the reverse side of the place where the connector insertion hole 11 is formed. The pedestal 12 comprises an outer peripheral portion having a flat boundary surface and a spacer insertion hole of circularly indented shape, and the center region of the spacer insertion hole is formed with a rectangular through-hole communicating with the connector insertion hole 11. Further, a resin spacer 13 provided with a pair of pin insertion holes 131 opening toward the connector insertion hole 11 is inserted into the spacer insertion hole and the rectangular through-hole of the pedestal 12. A plug assembly 2A equipped with a pair of electrode pins 21A serving as an electric signal input section is mounted on top of this spacer 13 and the outer peripheral portion of the pedestal 12 so as to sandwich a gasket 14 serving as a sealing material. Moreover, a peripheral wall 121 for ignitor unit attachment that is used to fix the ignitor unit is provided along the outer edge of the pedestal 12, and a peripheral wall 122 for case attachment that is used to fix a case charged internally with ignitor composition, gas generating agent and the like is further provided along the outer periphery of the peripheral wall for ignitor unit attachment.
The plug assembly 2A is equipped with a plug comprising a ring 22A made of metal and having a cylindrical side surface, the pair of electrode pins 21A that pass through this ring 22A, and an insulator 23 for fixing the pair of electrode pins 21A to the ring 22A. Note that the insulator 23 is constituted of glass, ceramic or other such insulator.
The ring 22A has a crimp margin at the portion mounted on the flat border surface of the pedestal 12 so that it is fixed by swaging the peripheral wall 121 for ignitor unit attachment of the holder 1A. The electrode pins 21A are electrically conductive members manifesting a cylindrical shape of finer diameter than the pin insertion holes 131 and extend in parallel with each other. On the side of insertion into the pin insertion holes 131, the electrode pins 21A pass through the insulator 23 and project a long distance, and project only slightly on the opposite side. And a resin sleeve 24 and a disk-shaped board 25 made of composite plastic are disposed on the ring 22A on this side where the electrode pins 21A project slightly. A resistor 26 composed of a thin film of nichrome alloy is provided on at least one side of the board 25 as a heating element. A primary charge 27 is placed on this resistor 26 and a coating 27a is additionally placed thereover.
Further, a hollow circular cylinder-shaped cylindrical body 28 is provided on the plug assembly 2A to cover the outer surfaces of the ring 22A and sleeve 24. Since the cylindrical body 28 is fixed by swaging the peripheral wall 121 of the holder 1A in the state fitted over the ring 22A, it is, like the ring 22A, formed along the lower edge with a crimp margin.
And the plug assembly 2A is fixed to the holder 1A by bending and crimping the upper edge portion of the peripheral wall 121 for ignitor unit attachments. Since the gasket 14 is press-fitted between the outer peripheral portion of the pedestal 12 and the lower edge of the ring 22A during this crimping, air-tightness is established between the holder 1A and the plug assembly 2A.
Further, the gas generator B is provided with a case 3A surrounding the ignitor unit comprising the holder 1A and the plug assembly 2A. The case 3A is an aluminum shaped part configured as a cylinder having a bottom that comprises an open portion having a thickness and inside diameter of a scale that can be fitted into a grooved portion of the holder 1A formed inside the peripheral wall 122 for case attachment and a bottom portion 3Ab radially formed with grooves so that it can be readily opened by the pressure of combustion gas. The open portion of the case 3A is formed with a peripheral edge portion 3Aa by fold-machining, and the peripheral wall 122 for case attachment of the holder 1A crimps the peripheral edge portion 3Aa to fix the case 3A in a state covering the upper side of the holder 1A. Moreover, the inside of the case 3A is charged internally with a prescribed amount of ignitor composition 31 and gas generating agent 32.
And in the gas generator B, when the impact at the time of a crash is applied to the electrode pins 21A as an electric signal, the resistor 26 between the pair of electrode pins 21A produces heat, and this heat ignites the primary charge 27, whereupon the ignitor composition 31 and the gas generating agent 32 are immediately inflamed. And then the combustion gas of the gas generating agent 32 breaks through the bottom portion 3Ab of the case 3A and discharges to the exterior, whereby the rapid winding-retraction means of the seatbelt is instantaneously activated by the pressure of the combustion gas.
Here, as with other vehicle parts, the need for cost reduction has risen also with regard to gas generators, and efforts are continuing at development worksites toward replacing expensive metal components with ones made of plastic and other synthetic resins. A challenge faced in this is how to give the parts replaced with synthetic resin ones the strength to withstand the pressure of the combustion gas while still maintaining the arrangement for rapidly retracting the seatbelt by efficiently releasing the combustion gas pressure from the bottom portion 3Ab so as to instantaneously drive a cylinder piston or a rotor. For example, in the case where the ring 22A and the insulator 23 in the gas generator B of FIG. 5 are replaced with synthetic resin ones, there is a risk of a problem arising under high-temperature condition, such as during a vehicle fire or the like, of this synthetic resin softening and the gas generating agent 32 inside the case 3A burning and projecting the electrode pins 21A outside from the side of the connector insertion hole 11.
[Patent Document 2]
On the other hand, Japanese Unexamined Patent Publication No. 2001-21293 (Patent Document 2), for example, teaches an invention wherein, with regard to the aforesaid plug, everything other than the electrode pins is replaced with synthetic resin, while the electrode pins are bent midway to expand the area of the electrode pins so as to maintain strength capable of withstanding the pressure of the combustion gas. The formation of the electrode pin bent portions can be expected to have an effect whereby the obstruction corresponding to the plug and its electrode pins do not disengage from the insertion hole provided on the vehicle body side.
[Patent Document 3]
Further, Japanese Unexamined Patent Publication No. 2004-114826 (Patent Document 3), for example, teaches a gas generator wherein the connector insertion hole provided in the holder is shaped like a pin-hole and used solely as a location for inserting the electrode pins, and the pair of electrode pins are twisted and provided integrally inside the holder 6. With this configuration, the twisted electrode pins are structured to catch in the direction of electrode pin extraction on a hole provided in a reinforcing member, so that the likelihood of the electrode pins flying outside the gas generator can be reduced.